It does sound a little neurotic to me, unless you have really badly installed piping in the wall. Does he have any thing he can point to that would suggest this could be a problem, or is he just worrying without any evidence to support it?

I'm a Plumbing & Heating contractor, and if your lug ell in the wall was installed with roofing nails or nails versus screws, and I would be a little concerned.

I constantly installed these new rain shower heads for customers, and the shower arm is loose as hell.

When I mention that to the customer, and recommend drywall gets cut opened so it can be fixed, every single time they politely decline, and disclaimer goes on the bill to protect my butt.

With a shower arm being loose and wobbling around, your bigger concerned is the weight of the shower head breaking the shower arm off in the pipe...then it's P.I.A. time to get it out.

Check your shower arm!

Thanks - I think we're going to exchange it for something lighter-weight. I don't know what the installation behind the wall was done with - the bathroom was remodeled 20 years ago, just before we bought the house (which is about 90 years old).